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Components of Cells
The Macromolecules

Fats and oils

Lipids consisting of three molecules of fatty acids covalently bonded to one molecule of glycerol are termed triglycerides (or triacylglycerols), but are more commonly known as fats and oils.

These molecules are the ultimate type of energy storage molecule because of their high calorific value and the fact that they can also thermally protect an animal's body from loss of heat in cold climates.

However, they are found in both animals and plants and constitute an important part of the human diet. The division into fats and oils is arbitrary and depends on the physical state of these molecules at room temperature. Those molecules that are usually solid at room temperature (plant or animal) are termed fats, while those that are liquids at room temperature are termed oils. These latter are usually found in plants, but fish also store liquid forms of triglycerides (fish oils).

Saturated Unsaturated
10 carbons 12 carbons 14 carbons 16 carbons 18 cabons 18 carbons 18 carbons 18 carbons
lauric myristic palmitic stearic oleic linoleic unsat.
Plant sources
peanut 8 3 56 26 7
olive 7 2 85 5
corn 1 10 3 50 34
cocconut 50 18 8 2 6 1
palm 2 41 5 43 7
Animal sources
fish oil 7 12 1 2 20 52
butter 15 2 11 30 9 27 4 1
lard 1 27 15 48 6 2
human 1 3 25 8 46 10 3

Solids and liquids

Solid fats usually consist of saturated fatty acids, whereas liquid oils are made largely of unsaturated acids, however this can be artificially manipulated to produce triglycerides with other desirable properties.

Natural lard (a fat from animal sources) melts at 30oC (above average room temperature), whereas natural olive oil becomes a solid only below -6oC. This latter is typical for valuable vegetable oils in general, but these oils can me made into semi-solids by partial hydrogenation of some of the double bonds found in the hydrocarbon chains.

Trans fats

This conversion is not without its problems, however. During the partial hydrogenation process, some of the remaining double bonds in the hydrocarbon parts of the molecule are changed into the trans configuration (isomerized).

Artificially modified vegetable oils are semi-solid and spread easily on bread right from the refrigerator, they have much longer storage lives that the liquid oils from which they were made, and they just "feel" better in the mouth when eaten. These are all desirable features, but when longer terms studies have been carried out on their effect it appears that a diet of unnatural trans-fats can be associated with some increase in heart problems, some cancers, diabetes and a tendency to obesity. There is even some indication that the immune and reproductive systems can be adversely affected.

© 2005, Professor John Blamire